Generally, as shown in FIG. 1, in a plant producing ready-mixed concrete, crushed stones, or the like, raw materials a.sub.1 -a.sub.5 such as sand, ore, and the like are transported from a raw material site b to raw material depots d.sub.1 -d.sub.5 of a plant c by means of a construction vehicle e.
Such a transporting operation is usually performed by an operator by running the construction vehicle e.
However, there are many cases where the operator's field of view is poor due to an operation at night, smog, or the like. In addition, the operator must often carry out the operation in a deteriorated environment where noise is intense or the place is heavily dusty, and although a simple loading, travelling and unloading operation is involved, the operation is very severe for the operator. Furthermore, there has been a demand for automatically travelling construction vehicles due to the frequent occurrence of labor accidents, a shortage of skilled workers, and an increasing number of higher-age workers.
In view of this situation, as disclosed in, for instance, Japanese Patent Laid-Open No. 100574/1978, an automatic travelling system of a construction vehicle is known in which guide lines are laid on a travelling road surface leading from a raw material site to raw material depots of a plant, and a guide signal detector is provided on a construction vehicle such as a dump truck, allowing the construction vehicle to travel automatically without being manned.
With this conventional system, since the dump truck always travel along a guide line while detecting the guide line by means of a guide signal detector disposed at a predetermined position, in order to change the travelling direction, it is necessary to separately provide a travelling direction changing-over means, and it is necessary to lay guide lines on all the predetermined travelling paths. For this reason, the number of guide lines increases, and the installation cost becomes high.
In particular, in cases where such a conventional system is applied to the aforementioned travelling system of a construction vehicle in a plant, as shown in FIG. 1, it is necessary to lay guide lines F.sub.1 -F.sub.5 on travelling road surfaces leading, for instance, from a main guide line L to each raw material a.sub.1 -a.sub.5, and in order to collect a raw material which is laid in a wide space, such as the raw material a1, it is necessary to lay auxiliary guide lines f.sub.1 -f.sub.3 branching from the guide line F1. Accordingly, since it is necessary to lay a multiplicity of guide lines on the vehicle-travelling road surface connecting the raw material site and the raw material depots d.sub.1 -d.sub.5, the installation cost increases remarkably, and the guiding operation is complicated, making it impossible to obtain desired guiding accuracy. Additionally, there is a drawback in that the place where the guide lines are laid is restricted.